Structures and articles are continuously being designed and produced to be larger, to be more complex, and to have increased strength. One such structure is a wind turbine. Wind turbines can include a plurality of blades rotationally coupled to a generator rotor through a hub. The generator rotor can be mounted within a housing or nacelle, which may be positioned on top of a tubular tower or a base. The housing or nacelle has significant mass which is fatigue loaded on the tower or base. Movement of the housing due to wind or other forces may result in loads such as reversing fatigue loads on the tower or base or on the nacelle or the housing.
Fatigue loaded structures or portions of structures may be subjected to numerous physical forces. Physical forces may result from factors including, but not limited to, environmental effects (such as sunlight being on only a portion of the structure at a time), operational effects, and/or exposure to changing conditions. For example, a wind turbine tower can sway due to changes in wind speed thereby creating tension and compression on the metal making up the tower. The nacelle may be exposed to similar forces from the rotation of the blades. Likewise, a generator housing or other portions of the wind turbine can be subjected to these and other forces. Over time, the tensile and compressive forces can form cracks. Upon being formed, the cracks can propagate with continued cycling of tensile and compressive forces. Ultimately, the cracks can lead to failure of the structure.
Often, weld points are one of the weaker parts of such structures. Generally, welds secure two metal portions together. For example, a first metal portion may be secured to a second metal portion thereby forming a desired structure, article, or part of the structure or the article. Welds can be formed by partially melting workpieces and optionally adding the filler material that cools to become a joint (the weld). Generally, energy is provided to partially melt the metal portions and/or an optional filler material that secures the metal portions. The energy can be provided by a gas flame, an electric arc, a laser, an electron beam, friction, ultrasound, or other suitable sources of energy.
The filler material used in the weld can affect the resistance to fatigue loading. The American Welding Society has promulgated design and fabrication Reference Standard AASHTO/AWS D1.5M/D1.5 “Bridge Welding Code” (Standard D1.5) for fatigue loaded structures. Standard D1.5 specifies the qualification, fabrication, and inspection requirements applicable to highway bridges. The specification is used as a basis for most carbon and low alloy steel fatigue loaded structures. Welds formed by carbon and low alloy steels can crack upon fatigues loading, depending on the amount of strain, number of cycles and the environment they are in. To remedy the cracking, frames and/or other suitable articles can be fastened to cracked structures. The frames and/or other suitable articles can be expensive and/or take substantial time to install. Furthermore, the frames and/or other suitable articles can still be susceptible to failure after being formed in compliance with standard D1.5, due to excessive loading conditions.